1. Field
The current invention is in the field of metrology of objects. Particularly, the invention relates to metrology of characteristics of conical shafts.
2. Related Arts
Magnetic disc drives are used for magnetically storing information. In a magnetic disc drive, a magnetic disc rotates at high speed and a transducing head “flies” over a surface of the disc. This transducing head records information on the disc surface by impressing a magnetic field on the disc. Information is read back using the head by detecting magnetization of the disc surface. The transducing head is moved radially across the surface of the disc so that different data tracks can be read back.
Over the years, storage density of media has tended to increase and the size of storage systems has tended to decrease. This trend has led to a need for greater precision, which has resulted in tighter tolerancing for components used in disc drives. In turn, achieving tighter tolerances in components requires increased precision in metrology systems for characterizing and parameterizing those components.
Air bearing spindle motors may be designed with conical bearing elements. In such instances, the bearing elements consist of conical shafts and corresponding sleeves. The materials used for making these shafts and sleeves include, but are not limited to, steel with highly polished surfaces. The angles of the cones only have a tolerance on the order of ±0.01° and have a crown on the surface with a height of 0.56±0.5 microns over the length of the surface. The crown is the amount of curvature on the outer surface of the cone. It is measured at the point where the distance between the surface of the cone and the imaginary line that represents the surface if there was no crown is greatest.
Existing methods of measuring the crown include using a contact surface profile measurement system. However these systems are slow, on the order of more than 120 seconds per measurement. The systems are also expensive, require a trained operator to properly align and measure the samples. Additionally, the contact method of measuring the samples can potentially damage the sample being measured.
Therefore, what is needed is a low-cost, accurate, and repeatable metrology system that is accurate, fast, and able to measure cone crown height tolerances of 0.56±0.5 microns over an 8 mm length and a repeatability (1-sigma) of 38 nm.